This invention relates to a method of manufacturing downhole electrical cable, particularly for use in providing electrical power and signals to downhole equipment.
In the hydrocarbon exploration and exploitation industry, there is a requirement to provide electrical signals from above ground and water to downhole equipment and subsea equipment.
One conventional method of manufacturing downhole electrical cable is to insert a leader wire into a steel tube. The leader wire is run through the length of the steel tube by pressuring the steel tube behind a piston head attached to the leader wire. When the leader wire has run through the entire length of the steel tube, the front of the leader wire is attached to a conducting wire, and the leader wire is pulled back through the steel tube, thus pulling through the conductor wire. Thus, the downhole electrical cable is formed.
However, there is a limitation on the length of steel tube through which the leader wire can be successfully pumped, as there are pressure losses over the length of the steel tube. Currently, the typical length requirement of downhole electrical cables is approximately 15,000 feet. With this method of manufacturing downhole electrical cable, it is normally not possible to produce any cables longer than this, as further increases in the fluid pressure may cause damage or failure of the steel tube.
It is also known to form the downhole electrical cable by seam welding the steel tube around the conductor. However, this has the disadvantage that the conductor, and insulating sheath that protects the conductor from the steel tube, may suffer degradation due to the heat produced by the seam welding process, which makes this existing method relatively expensive.